ON THE DEPENDENCE OF SOLAR-FLARE X-RAY SPECTRAL-LINE INTENSITY RATIOS OF HIGHLY IONIZED SULFUR, CALCIUM, AND IRON ON ELECTRON-TEMPERATURE, DIFFERENTIAL EMISSION MEASURE, AND ATOMIC PHYSICS

We derive values from solar flare spectra for the X-ray spectral line intensity ratio, w(Ca XIX)/w(Fe XXV), as a function of the temperature deduced from the dielectronic X-ray line j of Fe XXIV and the resonance line w of Fe XXV. The lines w and j represent the transition, Is2 1S0-1s2p 1P1 and Is22p 2P3/2-1s2p2 2D5/2, respectively. This intensity ratio is determined from a number of solar flares observed by X-ray Bragg crystal spectrometers flown on the P78-1 spacecraft and on the Solar Maximum Mission spacecraft. We also derive the relationship between the temperature determined from calcium X-ray lines and the temperature determined from iron X-ray lines for the same set of data. We compare these data with theoretical w(Ca XIX)/w(Fe XXV) ratios determined from parametric models of the differential emission measure, that are constrained by the calcium and iron temperatures. The model calculations show the effect of varying differential emission measure on the w(Ca XIX)/w(Fe XXV) ratio and allow us to determine which of three different published ionization equilibrium calculations for iron and calcium best fit the data. The functional relationship of w(Ca XIX)/ w(Fe XXV) with temperature and the relationship of the calcium and iron temperatures, determined from the data, also provide a method for estimating the approximate temperatures at which iron and calcium are formed in flares when dielectronic line ratios cannot be used. However, the method is not nearly as precise as the dielectronic technique. The model calculations are also used to predict functional relationships between spectral lines for flare X-ray lines of S XV and Fe XXVI.